The polyphenylene ether (oxide) resins are high performance engineering thermoplastics possessing relatively high melt viscosities and softening points, and which are useful in many commercial applications requiring high temperature resistance, including the formation of films, fibers and molded articles. The polyphenylene ether resins and methods of their preparation are described in U.S. Pat. Nos. 3,306,874 and 3,306,875 (Hay), U.S. Pat. Nos. 3,257,357 and 3,257,358 (Stamatoff), and elsewhere.
The polyphenylene ether resins are also known to be admixable with polystyrene resins, unmodified or modified with rubber, as disclosed in U.S. Pat. No. 3,383,435 (Cizek), to form blends which are extrudable or moldable into articles of various shapes and sizes.
Polyphenylene ethers are normally prone to undergoing discoloration, that is, yellowing, during processing at elevated temperatures and, after molding, upon exposure to ultraviolet (UV) light for extended periods. To improve the color stability of these polymers, stabilizing additives are sometimes included. For instance, Cooper, et al. in U.S. Pat. No. 3,925,509 disclose blends of polyphenylene ether resin and high impact, rubber-modified polystyrene resins which have been modified to be more ultraviolet light stable by adding a light absorbing compound selected from among hydroxybenzotriazoles, hydroxybenzophenones, and substituted derivatives thereof in combination with an organic nickel compound. In another case, Bennett in U.S. Pat. No. 3,563,934 discloses that an alkanolamine or a morphaline can be incorporated in a polyphenylene oxide resin to improve the flow and the thermal color stability of the polymer during molding, and to permit lighter colored objects to be more easily molded from the polymer.
The utilization of polyphenylene ether resin blends in a wider variety of commercial articles increases the likelihood that the polymer will be exposed to sunlight or strong indoor light during use, the UV radiation in either of which can cause discoloration of the plastic. It is desirable, therefore, to find additional ways of improving the UV-stability of the polymer with sacrificing other important properties.
Peter H. C. Shu has determined that combinations of an alkoxybenzophenone and a hindered amine provide unusually good improvements in the ultraviolet light stability of polyphenylene ether resins and blends. This development is described in the Shu application filed Dec. 22, 1983, now U.S. Pat. No. 4,555,538.